1. Field of the Invention
The invention relates to the creation of a mask for producing a printing plate.
2. Description of the Related Art
It is generally known that, in many technical areas, masks are used for surface treatment (printed circuitboard production) or else for printing processes (gravure printing, in which it is not printing plates which are fitted but the plate cylinder surfaces themselves which are prepared as printing plates) and lithographic processes. The objective is always, by using a material which has properties that differ from a substrate, that is to say a carrier of a material that differs from the mask material, to produce a specific structure (mask) on precisely this substrate. The mask produced in this way is then used as a starting point for further processes. For instance, it is intended to protect the substrate at specific points from the action of other substances.
The typical sequence of a previous method for creating a mask is subdivided into the following steps:
1. creation of a film with the structure information,
2. exposing a suitable photosensitive layer on a substrate through this film by means of a suitable light source,
3. development/cleaning in order to form the structure (mask) on the substrate.
Then, as a further step, for example etching or else the direct use of the mask can follow, for example as a printing plate in screen printing. By means of this mask, all the non-printing points are covered there. The printing ink passes through only at the open points of the mask.
As an alternative to the sequence previously described, the following is also already known:
1. applying an energy-sensitive layer to the substrate,
2. direct exposure or ablation of the structure by means of a suitable energy source, such as a laser or electron beam, which is variable in accordance with image information,
3. development/cleaning in order to form the structure (mask) on the substrate, if required.
This alternative is already used in the production of gravure plates. The mask is generally transferred to the gravure cylinder, a gelatin relief then generally remains on the said cylinder, its thickness corresponding to the tonal value of the diapositive or dianegative. During etching with ferric chloride, the iron salt diffuses through the gelatin and dissolves copper. The etching depth may be controlled largely via the different thickness of the relief, via the choice of appropriate etching bath concentrations and via the etching time.